Ultrasonic instruments, including both hollow core and solid core instruments, are used for the safe and effective treatment of many medical conditions. Ultrasonic instruments, and particularly solid core ultrasonic instruments, are advantageous because they may be used to cut and/or coagulate tissue using energy in the form of mechanical vibrations transmitted to a surgical end effector at ultrasonic frequencies. Ultrasonic vibrations, when transmitted to tissue at suitable energy levels and using a suitable end effector, may be used to cut, dissect, coagulate, elevate, or separate tissue. Ultrasonic instruments utilizing solid core technology are particularly advantageous because of the amount of ultrasonic energy that may be transmitted from the ultrasonic transducer, through an ultrasonic transmission waveguide, to the surgical end effector. Such instruments may be used for open procedures or minimally invasive procedures, such as endoscopic or laparoscopic procedures, wherein the end effector is passed through a trocar to reach the surgical site.
Activating or exciting the end effector (e.g., cutting blade, ball coagulator) of such instruments at ultrasonic frequencies induces longitudinal vibratory movement that generates localized heat within adjacent tissue, facilitating both cutting and coagulating. Because of the nature of ultrasonic instruments, a particular ultrasonically actuated end effector may be designed to perform numerous functions, including, for example, cutting and coagulating.
Ultrasonic vibration is induced in the surgical end effector by electrically exciting a transducer, for example. The transducer may be constructed of one or more piezoelectric or magnetostrictive elements in the instrument hand piece. Vibrations generated by the transducer section are transmitted to the surgical end effector via an ultrasonic waveguide extending from the transducer section to the surgical end effector. The waveguides and end effectors are designed to resonate at the same frequency as the transducer. When an end effector is attached to a transducer the overall system frequency may be the same frequency as the transducer itself.
The transducer and the end effector may be designed to resonate at two different frequencies and when joined or coupled may resonate at a third frequency. The zero-to-peak amplitude of the longitudinal ultrasonic vibration at the tip, d, of the end effector behaves as a simple sinusoid at the resonant frequency as given by:d=A sin(ωt)where:    ω=the radian frequency which equals 2π times the cyclic frequency, f; and    A=the zero-to-peak amplitude.The longitudinal excursion is defined as the peak-to-peak (p-t-p) amplitude, which is just twice the amplitude of the sine wave or 2 A.
Solid core ultrasonic surgical instruments may be divided into two types, single element end effector devices and multiple-element end effectors. Single element end effector devices include a variety of blade types such as ball, hooked, curved, and coagulating shears. Single-element end effector instruments have limited ability to apply blade-to-tissue pressure when the tissue is soft and loosely supported. Substantial pressure may be necessary to effectively couple ultrasonic energy to the tissue. The inability of a single-element end effector to grasp the tissue results in a further inability to fully coapt tissue surfaces while applying ultrasonic energy, leading to less-than-desired hemostasis and tissue joining. Multiple-element end effectors include a clamping mechanism that works in conjunction with the vibrating blade. Ultrasonic clamping coagulators provide an improved ultrasonic surgical instrument for cutting/coagulating tissue, particularly loose and unsupported tissue. The clamping mechanism presses the tissue against the vibrating ultrasonic blade and applies a compressive or biasing force against the tissue to achieve faster cutting and hemostatis (e.g., coagulation) of the tissue with less attenuation of blade motion.
Tissue welding is a technique for closing wounds and vessels and is applied in many surgical specialties. Tissue welding is a technique for closing wounds by creating a hemostatic seal in the wounds or vessels as well as creating strong anastomoses in the tissue. Ultrasonic surgical instruments may be employed to achieve hemostatis with minimal lateral thermal damage to the tissue. The hemostatis or anastomoses occurs through the transfer of mechanical energy to the tissue. Internal cellular friction breaks hydrogen bonds resulting in protein denaturization. As the proteins are denatured, a sticky coagulum forms and seals small vessels at temperatures below 100° C. Anastomoses occurs when the effects are prolonged. Thus, the ultrasonic energy in the vibrating blade may be employed to create hemostatic seals in vessels and adjacent tissues in wounds and to create strong anastomoses in tissue. Ultrasonic vibrating single or multiple end effectors, either alone or in combination with clamping mechanisms, produce adequate mechanical energy to seal vessels regardless of the temperature of the end effector and/or the tissue. To create strong anastomoses of the tissue, the temperature of the end effector and the tissue should be maintained below approximately 50° C. to allow for the creation of a coagulum to seal the tissues together without desiccating the tissues. Desiccation occurs through the cavitational effect. As the blade vibrates, it produces an area of transient low pressure at the tip of the blade causing fluid inside the cells to vaporize and rupture. Ultrasonic devices have not been successfully employed in tissue welding applications because of the need to control the temperature of the end effector and the tissue to achieve suitable hemostatis and anastomoses to weld tissue together. As the temperature of the end effector increases with use, there exists the likelihood that the tissues will desiccate without forming a proper seal. Conventional ultrasonic instruments ascertain the tissue state of desiccation as a feedback mechanism to address temperature control of the ultrasonic end effector. These instruments, however, do not employ the temperature of the end effector as a feedback mechanism. Therefore, there is a need in the art to monitor and control the temperature of an ultrasonic end effector to effectively enable the welding of tissues in wounds and/or vessels.
Ultrasonic end effectors are known to build up heat with use. The heat build up may be greater when the blade is used in a shears system with high coaptation forces. Coaptation in the context of ultrasonic surgical instruments refers to the joining together or fitting of two surfaces, such as the edges of a wound, tissue and/or vessel. Standard methodologies of cooling the end effector blade, such as running fluid through the blade while cutting, can have the undesirable effect of reducing the cutting and coagulating effectiveness of the blade. Thus, there is a need for an ultrasonic end effector blade that is capable of generating adequate heat for hemostatis, coagulation, and/or anastomoses tissue but that quickly cools when it is not in use.